Local gravitational environment a proxy for expanding Universe

May 19, 2016

The large-scale structure of the Universe provides one of our most powerful tests of the cosmological model, encoding a wealth of information about the expansion history of the Universe – imprinted as a standard ruler in baryon acoustic oscillations – and its gravitational physics – inferred from the growth of structure with time. Measuring the acoustic peak allows cosmologists to probe the dynamics of the Universe and the properties of the mysterious dark energy component.

However, the late-time gravitational interactions tend to erase the acoustic peak in the matter correlation function. Hence, cosmologists seek new ways to reconstruct the initial pattern of the galaxy clustering by mapping the displacement of galaxies. By shifting the position of the galaxies according to the local surrounding gravitational potential, they can infer the initial positions of the galaxies. Measurement of the matter correlation function on the reconstructed galaxy positions can thereby restore the shape of the acoustic peak.

As part of the CAASTRO Dark Universe research theme, Dr Ixandra Achitouv and Prof Chris Blake at Swinburne University of Technology have now found a direct correlation between the accuracy of the reconstructed position of galaxies and the scale used to infer the local gravitational potential which is required to reconstruct the positions. The researchers have also invented a new approach to analysing the reconstructed clustering of galaxies, based on the properties of the underlying matter density field. They show evidence that under-dense regions will carry more information on the acoustic peak compared to over-dense regions. Through their simulations, they were able to provide new estimates of the correlation functions which increase the accuracy of the acoustic peak measurement by 8%. This value may even be improved through future work, using sophisticated weighting schemes. The researchers will also investigate whether their model is readily applicable to non-standard cosmologies.